As i remember and this is a few years ago the last video interview as such would be certainly the monserrat video or defintely the jukebox one as i can't think of any other official source.
As for audio 'mike read queen for an hour' would certainly be the last audio interview or near enough , but i'm certain the daily mail published an interview in the summer of 91 i remember vividly because i was delivering daily papers all those years ago and it was by David wigg.
What i can't rememeber was the content of this interview but i can't seem them publishing a interview in a daily paper 4 years after it just doesn't make sense , it would have been in there sooner.
So to conclude then in my opinion there must have been a interview with freddie in the spring or summer of 91 by David wigg.
Is there anyway we can find out?.